For example, a significant change in a procedure might be the following: your lab manual wanted you to use a 10M solution of NaOH for a titration experiment, but you only used a 0.01M solution. That's a significant change.
...in a chromatography experiment, the lab manual described the use of a silica gel TLC plate, but instead you used a basic alumina TLC plate. That is a significant change.
These significant changes and should be described in the Experimental section of the lab report.
An insignificant change in procedure might be the following: the lab manual asked you to measure out 20 mL of solution using a 50 mL graduated cylinder, but instead you measured out 20 mL of a solution using a 100 mL graduated cylinder. Not a big deal and you do not need to mention this in the lab report.
Sketches of major experimental apparatus may be included, but are not necessary. For example you might want to draw make a diagram of a particularly complicated distillation set-up so that the reader will understand how the experiment was done, but such things as a balance, a computer, or a Bunsen burner are familiar to all modern chemists and do not need to be illustrated. All chemists have a good idea what they look like and how they operate. The point of the Experimental section is to clearly communicate to another how the experiment was set up and performed. A drawing of a computer is not going to further this goal, but a drawing of a piece of equipment that you designed yourself may be useful.
put in a sketch as an example